The present invention relates to a device for mounting a head, a charging electrode and deflection electrodes of an ink jet printer on a carriage and, more particularly, to a mechanism for supporting them in a secure and detachable manner independently of each other.
A carriage arrangement of a prior art ink jet printer is shown in a plan view in FIG. 1 and in a side view in FIG. 2. FIG 3 is a section along line III--III of FIG. 1.
As shown, a paper 10 is fed from the back of a platen 12 as indicated by an arrow X and therefrom toward a tray (not shown) by way of paper pressure rollers 14 and 16. A carriage 20 is mounted on and movable along parallel carrier shafts 22 and 24. A carriage harness 26 includes therein signal lines for controlling ink drops and tubes for supplying and collecting ink. Ink compressed by a pump (not shown) is admitted in a head 34 via the carriage harness 26, a supply tube 38, a filter 30, and a heater section 32. The head 34 is supported by a holder 36 together with a charging electrode 35 and resiliently backed by a leaf spring 38.
Among ink drops ejected from the head 34, those 40 charged by the charging electrode 35 are deflected by an upper deflection electrode 42a and a lower deflection electrode 42b to impinge on the paper 10. The other or non-charged ink drops 44 are caught by a gutter 46 to be led to the carriage harness 26 via a bore 48a formed though a collection holder 48, then being circulated by the pump. The carriage harness 26 is supported by a presser plate 50 and held between shock absorbing plates 52a and 52b. Each of the shock absorbing plates 52a and 52b is made of soft sponge and foamed material. Disposed in front of the carriage 20 is a pad 56 adapted to absorb by capillarity the ink mists which are collected by a mist absorption plate 54. The pad 56 is made of a plastic foamed material.
In the carriage 20 having the above construction, the holder 36 supporting the head 34 is mounted at its front portion on a holder base 58 to be pivotable about a shaft 60 in the perpendicular direction. The holder base 58, on the other hand, is mounted on the carriage 20 to be pivotable about a fulcrum 60a in the lateral direction. An adjusting screw 62 adjustably connects a rear portion of the holder 36 and that of the holder base 58, while a compression spring 64 constantly urges the holder 36 upwardly from below. The adjusting screw 62 may be manipulated to move the rear portion of the holder 34 upwardly or downwardly to vary a direction of ink ejection from the head 34 in the vertical direction. The holder base 58 is formed with a notch 66 in its rear portion. An eccentric screw 68 is received in the notch 66 with its shank abutting against the edge of the notch 66. When the eccentric screw 68 is rotated, the holder base 58 will angularly move about the fulcrum 60a to cause the holder 36 and, thereby, the head 34 to move to the right or left, varying an axis of ink ejection as desired.
As described above, the prior art carriage allows the direction of ink ejection from the head 34 to be adjusted both in the vertical direction and in the lateral direction so that the ejection axis of the head 34 can be oriented in a predetermined direction to insure stable image quality. Nevertheless, some problems have been left unsolved in such a carriage configuration as will be described.
Because the head 34 includes many stepped portions in its contour and has a large diametrical dimension and a small longitudinal dimension, it is backed by the spring 38 to be positioned in abutting engagement with shoulders of a collar 70. However, due to the vibration of the carriage 20 or like cause, the head 34 tends to tilt effecting the direction of ejection of ink drops from the head 34. Meanwhile, the head holder 36 is shaped concave toward the head 34 and is formed with an aperture 36a for the ejection of ink drops. The head 34 is built in or out of such a head holder 36 by inserting the charging electrode 35 in the concavity of the head holder 36, then positioning the collar 70, then mounting the head 34, and then loading the spring 38 to fix the whole construction at once. The gap between the head 34 and the charging electrode 35 in the assembled position is conrolled by cutting the collar 70 to a predetermined length.
The head and charging electrode arrangement discussed above is not fully acceptable in the following respects.
(a) The head has to be disassembled even when the charging electrode 35 is to be replaced with another.
(b) The charging electrode 35 is buried in the holder 36 to make it difficult to extend out a lead.
(c) Due to the use of the collar 70, its dimensional accurary has influence on the mounting accuracy of the whole head 34. Additionally, there is a fear of loosing the collar 70 in the event of replacement.
(d) Because the collar 70 is formed separately from the head holder 36, it is not easy to stably hold the head 34 in a predetermined position and, therefore, the head 34 might be mounted in an inclined position.
(e) The charging electrode 35 needs be made of porous sintered metal in order to absorb ink mist. In practice, use is made of a sintered member of stainless steel for the purpose of eliminating corrosion by ink (weak alkaline). For the same reason, soldering is unapplicable.
Meanwhile, in FIGS. 1 and 3, the upper deflection electrode 42a and the lower (ground) deflection electrode 42b are spaced several millimters from each other. The upper electrode 42a impressed with a voltage of several (-) kilovolts in order to deflect charged ink drops, developing several kilovolts of voltage across the upper and lower electrodes. Therefore, should the gap between the two electrodes 42a and 42b be reduced by some cause, discharging would occur to invite a machine error. For example, ink mists bouncing off the paper 10 or purging mists (positively charged) would become deposited on the upper electrode 42a (negative potential) to render the surfaces of holders 72a and 72b conductive or substantially conductive, resulting in discharging and, thereby, a machine error.
Further, ink drops impinging on the paper 10 during operation of the printer form mists and part of the mists is allowed into the carriage 20 via an opening 54a which is formed through the mist absobing plate 54. The mists inside the carriage 20 are deposited on the upper or negative deflection electrode 42a and the holders 72a and 72b therearound, the deposition spreading with the lapse of time. As shown in FIG. 3, the upper and lower deflection electrodes 42a and 42b are mounted respectively in central portions of the holders 72a and 72b which are in turn fastened to the carriage 20 by screws 74. As the ink mists penetrate the carriage 20 via the opening 54a of the plate 54 to smear the surfaces of the holders 72a and 72b until the gap between the upper and lower electrodes 42a and 42b becomes smaller than a certain value, discharging occurs to make deflection impossible and may even damage an electric circuitry associated with the head. While such a problem may be solved by increasing the distance between the facing surfaces of the holders 72a and 72b which hold the electrodes 42a and 42b, it cannot be increased beyond a certain limit.
It has been commonly practiced to amount the deflection electrodes 42a and 42b on their associated holder 72a and 72b by, as shown in FIG. 3, tapping the electrodes 42a and 42b to form threaded bores therein, and fixing them to the holders 72a and 72b by means of screws 76a and 76b. However, because the electrodes comprise sintered members of stainless steel taking into account the corrosion by ink as described, the rough or small-density particle structure makes the tapping and, therefore, quantity production difficult.